In the modern world of high speed rail travel with welded rails and in the increasing reliance on rail transport in the metropolitan corridor, rail condition becomes an increasingly important safety concern. Rail faults can occur as a break in the rail or as a fouling of the rails such as resulting from an object lying across one or both rails. Such faults can occur between the passage of trains and go undetected, particularly on long and winding runs or when operator attention may be diminished.
Various schemes are known to transmit signals along a railroad track by simple electrical conduction not dependent on transmission line characteristics for signaling or other purposes. In such instances rail integrity may correlate with the conductivity between rails. Such conductivity cannot then be used as a reliable indicator of the track condition for load carrying purposes.
In addition a track fault may develop or be more detectable during the loading when a train passes over the rails. It would be advantageous to be able to detect failure in this condition as well.